De Bruyne suffered the injury while training with City on Wednesday, though the full extent of the damage will only be known after further medical assessments.
The 27-year-old believes the injury to be similar to one suffered in an EFL Cup tie against Everton in 2016, which caused De Bruyne to miss nine weeks of football.
READ MORE: Walker - Man City want to dominate English football
It is understood that De Bruyne is likely be sidelined for a similar period of time and would therefore miss the start of City’s Champions League campaign.
De Bruyne attended the premiere of City’s new documentary series in central Manchester with team-mates on Wednesday night, arriving at the venue on crutches.
The Belgium international flew to Barcelona on Thursday morning to undergo initial assessments by Ramon Cugat, a doctor who regularly works with City’s injured players.
Patrick de Koster, De Bruyne’s agent, confirmed to Belgian media on Wednesday that his client felt the injury was similar to one suffered in 2016.
“It is the same one as previously, and he felt the same way,” De Koster said. “On that occasion no ligaments were torn, and that is the main thing. If that was the case he would be out for six to nine months.
“The medical tests will clarify how serious or not the injury is. It happened in training while he was standing on his own – he wasn’t involved in a challenge. It was an unfortunate accident.”